Moistureproof housing for piezoelectrtic elements



Nov. 16, 1948. c. H. WINTERMUTE 2,454,244

HOISTUREPROOF HOUSING FOR PIEZOELECTRI C ELEMENTS Filed Feb. 19. 1945 3062 2e FIG.2.

2o Wm 36" I: i WI] 40 I I III] FIG. 1.

V INVENTOR. CARLTQN H. W INT ERMUTE WM 3, M

ATTORNEY Patented Nov. 16, 1948 MOISTUREPROOF HOUSING F OR PIEZO-ELECTRIC ELEMENTS Carlton H. Wlntermute, Newark, N. J.

Application February 19, 1945, Serial No. 578,750

14 Claims. 1

This invention relates to piezo-electric elements which are usecf in thecommunication circuits for stabilizing the frequencies of oscillatorsand filter circuits; more particularly, the invention relates to ahousing for such elements.

With the widening of the frequency spectrum of the carrier frequencywaves, the requirements imposed upon the piezo-electric elements, fromthe point of view of their frequencystability and constancy of theiractivity, have been increasing at a very rapid rate, and they nowreached such a level that even the presence of an insignificant amountof humidity in the housings surrounding and supporting the crystal wasfound to be detrimental to the maintenance of constant frequency andactivity by the piezo-electric elements, Prior to the elimination of theso-called aging phenomenon which manifests itself as changes in thenatural frequency of vibration and decreasing activity of thepiezo-electric elements after completion of the lapping process, thepresence of water vapor in the air surrounding the piezo-electricelements had two distinct and independent detrimental effects. Oneeffect was the physical and chemical interactions between the watervapor and the disoriented layer produced on the quartz plates during thelapping process, these interactions producing the above mentionedfrequency changes and loss of activity. Evolution of a process foreliminating the aging phenomenon (see U. S. patent application of V. E.Bottom, Processing of piezo-electric elements, S. N. 575,109),eliminated the disoriented layer on the surfaces of the finished plates,and, as a. consequence, eliminated the first effect. However, the secondeffect of the water vapor still remained, and its elimination becameeven more important with the agingfree elements, if one were to exploitfully the superior frequency and activity stabilities of the elementsproduced by the new process. The second effect of the water vapor is asfollows: if the moisture present in the air surrounding thepiezo-electric plate is allowed to condense on the surfaces of theplate, it acts as a damping means, decreasing the activity of the plateand broadening its frequency response, thus destroying in large measureits usefulness as a frequency control element. This is especiallyharmful at high frequencies.

The invention discloses a moisture-proof, hermetically-sealed housingfor the piezo-electric element and its mountings, so that if the elementis assembled in the environment of low relative humidity, it will retainits desirable frequency control characteristics, as well as itsactivity, even when the entire unit is operated under most unfavorable,relative humidities outside the housing. The housing is also providedwith an opening for replacing the air within the housing with an inertgas, whereupon the housing is sealed with a metallic seal. When thehousing is filled with the inert gas, the humidity factor is eliminatedaltogether.

Generally, the crystal holders known and used in the communication artare constructed in two parts: one being a base, and the other a hollowcover connected to the base. Sometimes the base is extended so as toform five sides of a box used for holding the piezo-electric plate andits mounting, the cover itself representing a plate fitting into arecess provided for this purpose in the four sides of the box. The box,cover, and base, as a rule, are made of fiber or synthetic resin, thethree elements of the unit being made air-tight by providing a gasketbetween the cover and the box. This type of connection between the boxand the cover is not adequate to prevent water vapor from leaking intothe unit through the joint, and the synthetic resin used for making thebase and the cover, as a rule, is unfavorably affected by high humidityof the surrounding air, so that when the units are exposed to highhumidity over .a long period of time, the water vapor eventuallypenetrates the inner chamber of the unit. 1

The invention discloses a housing for the piezo-electric element whichis capable of withstanding exposure to high humidity for an indefinitelength of time, thus protecting the resonator and the metallic elementsused for mounting this resonator within the housing. The invention alsodiscloses a mounting for the piezoelectric plate, the mounting beingparticularly suitable for its use in connection with the disclosedhousing.

It is, therefore, the object of this invention to provide amoisture-proof housing for the piezoelectric elements.

It is the additional object of this invention to provide apiezo-electric unit including a hermetically-sealed housing filled withan inert gas, and a mounting for the piezo-electric plate fit: ting intothe housing.

The novel features which are believed to be characteristic of theinvention are set forth in the appended claims. The invention itself,however, both as to its organization and method of construction,together with the further objects and advantages thereof, may best beunderstood by reference to the further description in connection withthe accompanying drawing, in which:

Figure 1 is an exploded, perspective view of the unit; and

Figure 2 is an elevational view of the unit with one side of the cover,and one half of the ceramic frame and base removed.

Referring to the drawings, the holder includes a base frame i stamped ofa Kovar metal (54% iron; 28% nickel; 18% cobalt), this metal having thethermal coefiicient of expansion equal to the thermal coeflicient ofexpansion of Pyrex glass, 6-705 F. M. (borosilicate glass). Frame i0 isprovided with two cylindrical extensions Ill and I2 for accommodatingconnecting pins 53 and M which are held in the central position withinthe openings of the frame by glass seals it and it. The glass seals maybe made so as to extend across the entire frame ill in the upper portionof the seal, as illustrated in Fig. 2. The cylindrical extensions Illand 62 provide positive seats between the pins and the frame, theresuiting structure possessing the desired rigidity and mechanicalstrength to withstand the stresses imposed upon them when the unit isinserted and taken out of the radio sockets. Pyrex glass, such as 3-705F. M., having the same thermal coefficient of expansion as f iovermetal, and. capable of wetting Ko'var is used for insulativelyconnecting the frame and the pins to each other, the pins being alsomade of .flovar metal. The upper portion of frame it) is provided with aflaring-out flange 28 which is so dimensioned that a metallic cap fitsinto the flaring-out portion of frame as illustrated more clearly inFig. 2. Cap it is made of any noncorrosive material suitable for drawingand stamping operations, such as stainless steel or brass. Upon theinsertion of the crystal and crystal mounting into the housing, cap issoldered to base ill by a soldering joint The housing, therefore,consists of pins l3 and i which are secured to frame ill by means of theglass seals l5 and iii, and cap Zil which is soldered to frame iii. Thetop of cover 26 is provided with an opening 2 t which is used forevacuating the holder therethrough, and filling the holder with an inertgas, such as hydrogen, helium, or neon upon its evacuation, hydrogen,helium, and neon being fairly good conductors of heat and tending tolreep the unit dry. The opening also acts as a vent for the expandingair within the housing during the soldering operation of the cover tothe frame. Hole 24 is solder-sealed after the unit is filled with gas.The suggested combination of metal and glass, such as Kovar-Pyrex, isthe one that gives especially good results because, as mentioned before,the two substances have the same temperature coefficient of expansion,and it is capable of withstanding abrupt temperature changes withoutdeveloping any mechanical failures. Moreover, the Kovar-Pyrexcombination offers certain production advantages, since it does notrequire any special annealing subsequent to the completion of thesealing operation, and gradual cooling of the seal is all that isrequired. The invention is not restricted to this particularcombination, and, therefore, other metal-to-glass seals may also beused, although their resistance to the thermal shocks, even if ill No. 4alloy (iron-nickel-chrome alloy in combination with "Corning glass G-l;Sealmet of Allegheny Ludlum Steel Company in combination with Corning"glass (3-12, and other metal-toglass seals known to the art. Theall-metal container with a glass seal at its base will not absorbmoisture, nor allow any leakage of moisture into the inner chamber ofthe housing, thus producing a hermetically-sealed crystal housing.

Any desired crystal mounting may be used in connection with thedisclosed housing. However, Figs. 1 and 2 disclose a preferred form ofmounting which possesses certain advantages outlined below. The mountingconsists of a ceramic case formed by two ceramic side members 25 and 28which, when closed, match each other with the flat surfaces El, 23, 29,and Sil. The side members are so proportioned that they loosely fit intothe cover Bil of the housing, as illustrated in Fig. 2. The side membersare provided with rectangular recesses, such as recess 32, a similarrecess being provided in the side member 28. Mounted between the sidemembers 25 and it are a piezo-electric plate 34, stainless steelplateelectrodes 35 and 35;, a helical spring to and two Phosphor-bronzeconnectors 52 and t4, the stainless steel plates 36 and contacting theplate, the connector resting between plate 38 and side member Eli, whileconnector id is placed between plate 36 and spring ill. as illustratedin Fig. 2, spring Ml maintaining positive contact between the connectorsand the steel plates, as well as between the steel plates and thepieZo-electric plate. Plate rests on connector l2 whose thickness isslightly greater than the depth of the recesses in the ceramic members25 and 26 for accommodating them. This recess is illustrated as a flatsurface 33 between the side shoulders 46 in the side member The ceramiccase, together with its contents, rests on a ceramic base '18 shaped astwo integral elliptical disks Sill and 52 provided with two slits and 56used for passing the electrodes 32 and it through the ceramic base, asillustrated more clearly in Fig. 2. The connectors are provided withlugs 58 and fit which fit over the protruding upper portions of the pinsM and (I3, respectively. Irrespective of the type of crystal mountingused, the pins i3 and M, or the two conductors connected to them, mustprotrude into the housing, as illustrated in the Figs. 1 and 2, in orderto establish the connections between the mounting and the pins. Thelugs, the upper portion of frame ill, and the protruding portions of thepins it and it are pretinned before the assembly of the unit. The unitis assembled by sliding the piezo-electric plate, the electrodes, andspring Ml into the ceramic case, then sliding the ceramic case intocover 20. Connectors t2 and M are then inserted into slits 55 and fit,and ceramic base 38, thereupon, is placed on top of pins i3 and M, thelugs 58 and 6!] fitting over the upper portions of the pins, asillustrated in Fig. 2. Cover 2d is then placed over the ceramic base 48in such a manner that the upper portions of connectors 42 and 44 slideinto engagement with the electrode-plates, and cover 20 slides into theupper portion of frame 10. soldered joints between frame Ill and cover20 (joint l8), and pins I3, l4, and lugs 60 and 58 are made in a highfrequency furnace, opening 24 acting, during this soldering operation,as a vent hole for the heated expanding air within the holder which isfree to escape from the holder without interfering with the formation ofnonporous solder joint l8. It has been discovered the electricalcontacts.

that the absence of such a vent hole during the soldering operationforces the heated air to escape through the molten solder of Joint l8,thus creating a porous solder joint which is not capable ofhermetically-sealing the housing. The next step in assembling the unitconsists of evacuating the holder and filling it with hydrogen or anyother inert gas (helium, neon argon, etc.), whereupon opening 24 issealed with a solder seal 62.

The advantages of the disclosed unit may be summarized briefly asfollows: it is not afiected by external humidity and is capable ofmaintaining very high, external leakage resistance even when surroundedwith air, saturated with water vapor; the unit is capable of resistingmechanical and thermal shocks, the mechanical shocks being absorbed bymaking the ceramic case as two, split side members 25 and 26 which candisplace, with respect to each other and with respect to the housing,against friction. The same is true of the ceramic base 48. Suchdisplacements do not alter the positive nature of The split constructionof the ceramic case also facilitates the use of precise dies resultingin finer production tolerances. Moreover, assembling of the unit andalignment of the mounting is facilitated by using the disclosedarrangement of parts.

It is believed that the construction of the housing, as well as theadvantages thereof, will be apparent from the foregoing description. Itshould be understood that while the invention has been described in onepreferred form reasonable changes and modifications may be made withoutdeparting from the spirit of the invention, as sought to be defined inthe following claims:

What is claimed is:

l. A piezo-electric unit comprising a moistureproof, hermetically-sealedhousing including a metallic cap and a metallic, glass-sealed base withtwo connecting pins protruding into said housing through said base; apiezo-electric plate and a mounting for said plate surrounded by saidhousing, said mounting including a mounting-base resting on theprotruding portions of said pins and made of electrically insulatingmaterial, and a case made of electrically insulating material, said caseresting on said mounting-base and fitting into said cap, saidmounting-base and said case forming an inner chamber within saidmounting for holding said piezo-electric plate, the electrodes for saidplate, and connectors protruding into said chamber through saidmounting-base, the upper end of said connectors making electricalcontacts with said electrodes, and the lower end of said connectorsmaking electrical contacts with said pins.

2. A piezo-electric unit as defined in claim 1 in which said casecomprises two symmetrical side members, and said mounting-base comprisestwo integral plates, one of said plates resting on said pins, and theother plate protruding into said case so as to act as a support for saidpiezoelectric plate and said electrodes.

3. A piezo-electric unit as defined in claim 1 which further includeslayers of soldering metal deposited respectively on the upper portion ofsaid metallic base, theprotruding portions of said pins, the lower endsof said connectors, and the lower portion of said metallic cap, saidlayers being used for establishing a metallic seal between said metalliccap and said metallic base, and soldered connections between said pinsand said connectors.

4. A piezo-electric unit as defined in claim 1 which further includeslayers of soldering metal deposited respectively on the upper portion ofsaid metallic base, the protruding portions of said pins, the lower endsof said connectors, and the lower portion of said metallic cap, saidlayers being used for establishing a. metallic seal between saidmetallic cap and said metallic base, and soldered connections betweensaid pins and said connectors during the soldering operation of saidunit, and an openin in said metallic cap, said opening acting as a ventduring said soldering operation.

5. A piezo-electric unit as defined in claim 1 which further includes anatmosphere of inert gas filling said housing, and an opening in saidmetallic cap, said opening acting as a vent during the solderingoperation of said cap to said base, and as a means for replacing the airin said housing with said inert gas upon the completion of saidsoldering operation.

6. A moisture-proof housing for a piezo-electric element comprising ametallic cap and a base, said base including a stamped, metallic frame,said frame forming the external member of said base, the upper portionofsaid frame making a sliding fit with said cap, and the lower portion ofsaid frame having two bottom openings, two pins for establishingelectrical connections of said element, a glass seal filling the bottomportion of said frame, and holding said pins in concentric relationshipwith respect to said openings,,the,'inner ends of said pins protrudingthrough said glass seal into said housing for establishing saidelectrical connections with the mountings of said piezo-electricelement, said frame, pins, and glass seal having substantially" equalthermal coefficients of expansion, anda solder seal between said cap andsaid frame for making said housing moisture-prom.

7. A moisture-proof housing for a piezo-electric element as defined inclaim 6 which also includes an opening in said cap, said opening actingas a vent for expanding heated air within said housing when said solderseal is being made, an atmosphere of inert gas filling said housing,said gas replacing, through said opening, said air upon theestablishment of said seal, and a metal seal applied to said openingupon filling said housing with said gas.

8. A moisture-proof housing for a piezo-electric element as defined inclaim 6 which further includes hydrogen gas filling and sealed withinsaid housing. 1

9. A moisture-proof hou s ing for a piezo-electric element as defined inclaim 6 which further includes helium gas filling and sealed within saidhousing.

10. A moisture-proof housing for a piezo-electric element as defined inclaim 6 which further includes neon gas filling and sealed within saidhousing.

11. A moisture-proof housing for a piezo-electric element comprising ametallic cap, a base including-a stamped, metallic frame, the upperportion of said frame being dimensioned to make a sliding fit with saidcap and the lower portion of said frame having two cylindricalextensions,

'two pins for establishing electrical connections with said element, aglass seal filling said cylindrical extensions and extending to a levelapproximately midway between the upper and lower edges of said-frame,the upper surface of said seal forming the floor surface of saidhousing, said seal holding said pins in centrally disposed baseincluding a frame, said frame forming the external member of said base,the upper portion of said frame making a sliding fit with said cap, thelower portion of said frame having two bottom openings, two pins forestablishing electrical connections of said elements, an insulation sealfilling the bottom portion of said frame, and holding said pins inconcentric relationship with respect to said opening, the inner ends ofsaid pins protruding through said insulation seals into said housing forestablishing electrical connection with the mountings of said element,said frame, pins and insulation seal having substantially the samethermal coefficient of expansion, and sealing means between said cap andsaid frame for making said housing moisture-proof.

13. A moisture-proof housing for a piezo-electric element comprising acap and a base, said base including a frame, said frame forming theexternal member of said base, the upper portion of said frame making asliding fit with said cap, the lower portion of said frame having atleast one bottom opening, at least one pin for establishing anelectrical connection of said element, an insulation seal filling thebottom portion of said frame, and holding said pin within said opening,the inner end of said pin protruding through said insulation seal intosaid housing for establishing electrical connection with a mounting ofsaid element, said pin, frame, and insulation seal having substantiallythe same thermal coeflicient of expansion, and sealing means betweensaid cap and said frame for making said housing moisture-proof.

14. A moisture-proof housing for a piezo-electrio-element comprising acap and a base, said base including external means for receiving saidcap, said base having at least one opening therein, and at least oneterminal member for establishing an electrical connection of saidelement, an insulation seal filling said opening and holding saidterminal member within said opening, one end of said terminal memberprotruding through said insulation seal into said housing forestablishing electrical connection with a mounting of said element, saidbase, terminal member, and insulation seal having substantially the samethermal coeiiicient of expansion, and sealing means between said cap andsaid base for making said housing moisture-proof.

CARLTON H. WINTERMUTE.

REFERENCES CITED The following references are of record in the file ofthis patent:

